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Briefly, the HDR process involves merging several exposures of a given scene into a 32-bit HDR source file, which is then "tone mapped" to produce an image in which adjustments of qualities of light and contrast are applied locally to the HDR source image (not globally), resulting in an image with amazing detail throughout the tonal range -- capturing highlights and shadows that would otherwise be lost in a traditional Low Dynamic Range (LDR) image. (If you are interested in the science and algorithms behind the process, here is a good explanation.)
Depending on the source images, and depending upon the settings used in tone mapping, the results you can achieve range from photorealistic to images that have a wealth of detail, but look illustrated or overworked and cross the line from photographic to photograph-based graphic. For this story, we're sticking with photorealistic images and results. We'll explore how to make HDR images in HDRSoft's Photomatix ($99, free demo available), and Adobe Photoshop CS2 and Bridge ($649, free trial available), with step-by-step instructions and examples, and also analyze the strengths and weaknesses of each program. We'll look at some images and situations that work well for HDR, and some situations where traditional Photoshop techniques may yield better results.
Be warned: even with a fast computer, we're dealing with huge files, and tons of processing time, especially with full-size images. We strongly suggest that if you wish to try HDR imaging out, practice on screen-sized images. Fortunately, both of the programs we're exploring allow you to save tone mapping settings and re-apply them to other images (such as a full-size version of your low-resolution tests.)
HDR imaging involves multiple files, multiple steps, and sometimes less-than-intuitive program paths from start to finish. It is easy to miss a step and get frustrated and confused (believe me, I know this all too well). But with a little practice, experimentation, and learning the HDR workflow, you may find yourself rewarded with great HDR images. We're going to take a look at the standalone program Photomatix first.
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